Process for the manufacture of cylinders

ABSTRACT

IN THE NANUFACTURE OF CYLINDERS COMPRISING TWO CONCENTRIC CYLINDRICAL SHELLS WITH AN INTERPOSED CORE COMPRISING RADIALLY EXTENDING GAS-FILLED CELLS A THIN SUPPORT LAYER WHICH IS POROUS TO THE MATERIAL FROM WHICH THE INNER SHELL IS SPUN CAST IS APPLIED TO THE INNER FACE O THE CORE AND THE INNER SHELL IS SPUN CAST AGAINST THE SUPPORT LAYER.

June 11, 1974 R. c. TENNYSON PROCESS FOR THE MANUFKCTURE 0F CYLINDERSFiled Oct. '24, 1972 INVENTOR.

RODERICK C. TEN N YSON KM fiydd PATENT AGENTS United States Patent M3,816,582 PROCESS FOR THE MANUFACTURE OF CYLINDERS Roderick C. Tennyson,12 Shasta Dn've, Thornhill, Ontario, Canada Continuation-impart ofabandoned application Ser. No.

69,835, Sept. 4, 1970. This application Oct. 24, 1972,

Ser. No. 300,018

Int. Cl. B29c 5/08 US. Cl. 264-255 6 Claims 'ABSTRACT OF THE DISCLOSUREIn the manufacture of cylinders comprising two concentric cylindricalshells with an interposed core comprising radially extending gas-filledcells a thin support layer which is porous to the material from whichthe inner shell is spun cast is applied to the inner face of the coreand the inner shell is spun cast against the support layer.

CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of my application Ser. No. 69,835, filed 4thSeptember 1970, now abandoned.

Field of the invention This invention is concerned with a new processfor the manufacture of cylinders of the type comprising at least twoconcentric cylindrical shells and an interposed core.

At the present time there is a need for the production of accuratelyformed cylinders of high strength and light weight, for example, invarious aerospace applications. These desirable properties of strengthand weight can be achieved, for example, by forming the cylinder from apair of spaced concentric shells with an interposed core, but theproduction of such cylinders hitherto has involved complex and expensiveproceses employing complex and expensive apparatus.

DEFINITION OF THE INVENTION It is an object of the present invention toprovide a new process for the manufacture of cylinders of the typespecified.

It is a more specific object to provide a new process for themanufacture of cylinders of the type specified and comprising spun-castconcentric inner and outer cylindrical shells with an interposed core ofthe honeycomb type.

In accordance with the present invention there is provided a process forthe manufacture of a cylinder comprising spaced inner and outerconcentric cylindrical shells of which at least the inner shell isformed of fiowable solidifiable material and *which have bonded theretoan interposed core of open-cell type material disposed with the cellends opening radially and closed by the shells, the process includingthe steps of:

(a) providing the said outer shell,

(b) applying and bonding to the inner cylindrical surface of the outershell a layer of said core material,

(c) applying to the inner surface of the core material layer a thinsupport layer porous to the solidifiable material and which is effectiveto prevent excessive percolation of the flowable material into the corematerial, but is sufficiently porous to be completely impregnated withthe flowable material.

(d) rotating the outer shell, the core material and the support layerand forming the inner shell against the said support layer by spincasting from the said fiowable, solidifiable material under settingconditions for the material, with the speed of the said rotation suchthat the solidifiable material penetrates the support material andPatented June 11, 1974 solidifies therein without excessive percolationof the solidifiable material into the core material.

DESCRIPTION OF THE DRAWINGS FIG. 2 is a partial end view to showparticular features thereof, and

FIG. 3 is a cross section through part of the wall of a cylinderproduced in accordance with the invention, in order to show thestructure thereof, the drawing being to an enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical simple spin-castingapparatus for the operation of processes of the present inventioncomprises a rigid rectangular base frame 10, having two parallel spacedgenerally-triangular standards 11 and 12 upstanding verticallytherefrom, each of the standards carrying a respective self-aligningbearing 13 and 14 mounting a relatively massive, rigid shaft 15 forrotation about a horizontal axis. One end of the shaft 15 carries apulley 16, which is connected by a belt 17 to a variable speed electricdriving motor 18 mounted on the base frame.

A cylindrical mould in which the cylinders are formed comprises atubular body 19 provided with circular end plates 20 and 21 removablyfastened to the body, as by machine screws 22. The mould is mounted onthe shaft 15 coaxially therewith by two flanged members 23 bolted to theend plates, these members being rotatable with the shaft 15 to rotatethe mould, and at least one of them being movable axially along theshaft to permit the mould to be dismantled from the shaft.

The manufacture of accurately-formed cylinders of uniform externaldiameter requires the use of a mould drum with an accurately-formedinternal surface that is truly co-axial with the shaft. Preferably, thedrum 15 is formed of a transparent material, such as methyl methacrylateplastic, so that the progress of the process can readily be observed. Inan initial step of the operation of the processes of the invention themould drum internal cylindrical surface is prepared to the requiredaccuracy.

Each end plate 20 and 21 is provided with two adjustable mass balanceweights 24 and 25, which may comprise two bolts each mounted in arespective screw-threaded aperture, the two apertures being disposedrespectively on radii which are at right angles to one another. Theweights also comprise washers of different sizes and thicknesses, whichcan be clamped between the bolt heads and the end plates.

In another arrangement the bolts 24 and 25 are movable in respectiveradially-extending slots 26 and 27 (shown in broken lines), the slotsbeing disposed with their longitudinal axes at a right angle to oneanother. In such an arrangement each end plate can be provided with adiametrically-opposed similar slot to maintain the primary balance ofthe plate and to permit movement of each balance weight to the otherside of the longitudinal axis, if that should be necessary. Othermethods of achieving static balance adjustment of the mould drum will beapparent to those skilled in the art.

The internal surface of the drum may first require a cleaning operation,as by subjecting it to the washing action of a solvent, e.g. alcohol;the drum and shaft combination is then statically balanced as accuratelyas possible and, if the balancing has not been carried out in situ, itis then remounted in the bearings 13 and 14.

A thin layer of a suitable releasing agent is first applied to the innercylindrical surface of the mould drum, preferably by spin-casting so asto avoid any change in the accuracy of formation of the surface. Thematerial can be applied in the form of a solution inserted via a pouringhole 28 in one end plate, the solvent being evaporated while the drum isrotated at an appropriate rate.

The outer circular cross-section cylindrical shell 30 (see FIG. 3) isthen spun-cast in the mould from any suitable flowable solidifiableplastic material of viscosity low enough in the flowable state to flowover the mould interior and form a uniform layer. More than one layercan be employed in the formation of the shell, the subsequent layerspreferably being applied before final curing of the immediatelypreceding layer so that they bond strongly together. If necessary, therate of setting of the plastic material is increased by the applicationof heat to the drum, for example by means of diametrically-opposed rowsof radiant heaters 29.

In some embodiments the outer shell may be of composite material, forexample by incorporating a fibrous material therein. Such compositematerials are formed by adding chopped fibers of material such as glass,carbon or boron during any part of the shell formation process, or byadding one or more layers, in fabric or non-woven mat form, insertedinto or between any of the layers of the shell. Any of the addedcompositing materials can be pre-wetted with plastic material tofacilitate its incorporation. With appropriate values of angularvelocity of the drum to produce suflicient centrifugal force, trappedair bubbles are driven from the liquid plastic and, in the case ofcomposites, several layers can be completely impregnated during one spincasting operation. Additional thickness can be obtained by successivespin-casting of new layers. Good bonding between juxtaposed layers isachieved if proper curing times are used, the additional layers areadded at appropriate times during the curing of the preceding layers,and the newly formed surfaces of the layers are maintained free fromcontamination.

In these particular embodiments the open-cell type material forming thecore 31 is a sheet of honeycomb configuration, comprising juxtaposedopen-ended hexagonal cells with the longitudinal axes of the cellsperpendicular to the general plane of the sheet. Depending upon thecylinder radius and the stiffness of the honeycomb sheet, the corematerial can be inserted in the form of a single sheet, with alongitudinal butt joint, or as several butting longitudinal segments.Prior to insertion of the core into the mould a very thin layer of theliquid resin forming the outer shell is applied to the shell innersurface and/or to the honeycomb sheet surface that contacts the shellinner surface. By the use of a high enough speed of rotation the corematerial is urged radially outward and held in complete contact with theouter shell while the plastic sets or cures, thereby achieving excellentbonding of the core to the outer shell inner surface. In another processthe core material may be bonded to the outer shell by permitting theshell, or the innermost layer thereof, to cure to the extent that it isself-supporting if the drum is stopped but is still tacky. The corematerial is then placed in position and the drum spun while the resincure is completed and secures the core layer to the shell.

A thin, porous support layer 32 is now applied to the inner surface ofthe core material layer. The exact porosity required for this layer toproduce the most effective results for the particular process canreadily be determined by simple experimentation. Suitable materials arefor example, thin tissue paper, kraft paper, bond wrapping paper, finemesh materials, and thin fabrics such as glass fibre fabric. The supportlayer material will usually be sufficiently thin that it can bepermitted to form a longitudinal overlap join in the mould.

The support layer may be pre-impregnated with the same solidifiableliquid material that is used for forming the inner shell, or with aplastic material compatible therewith. After application of the supportlayer the mould is rotated to press the layer into close contact withthe adjacent surface of the core layer.

Any plastic material of the support layer may now be permitted to cure,for a predetermined period. Immediately upon placement of the supportlayer or at any time before full curing of any plastic material in thesupport layer can take place, the inner shell 33 is formed byspin-casting at least one layer of flowable solidifiable materialagainst the support layer, which is effective to prevent excessivepercolation of the flowable material into the core material, but issufficiently porous to be completely impregnated with the flowablematerial if not already in this state, so that it is substantiallycompletely incorporated in the inner shell upon solidification of thematerial. The inner shell 33 is thereby strongly bonded to the adjacentsurface of the core layer 31, despite the presence of the interveningsupport layer. With many of the materials used for the support layerinspection of the resultant product shows that the support layer hasbecome translucent, and this phenomenon can be used as an indication ofthe etxent to which complete penetration of the support layer by plasticmaterial has taken place. Thus the absence of the desired completepenetration in any spot will be revealed by the non-translucentappearance of that part of the support layer. Moreover, it is frequentlyfound that suflicient plastic material has penetrated the support layerto form a meniscus in the immediately adjacent ends of the open cells ofthe core material, ensuring particularly strong bonding between the coreand the inner shell.

Upon the formation and curing of the final layer of the inner shell thecylinder can be removed from the mould cylinder 19 by any convenientmeans, for example by use of an end plug urged by a hydraulic jack, therelease layer permitting this operation without damage to the mouldinner surface. The cylinder is immediately ready for use for manypurposes, or it may require that the annular ends be sealed by anysuitable means. The resultant cylinder may be slit longitudinally toform corresponding laminated curved panels, whose edges are then sealed.

Table 1 below shows materials that have been used in the successfulproduction of cylinders by processes of the invention and which may beused in combination with one another.

TABLE 1 Shell wall materials:

Hysol XC9'-C419 resin of Hysol Corp. with #3646 hardener about 300 to500 centipoise viscosity. Araldite 502 epoxy resin of Ciba Products Co.with #951 hardener (about 400 centipoise). Polyester of about 800centipoise viscosity.

Core material:

Nomex HRH-10 of Hexcell Aerospace Corp. Flex-core 5052 aluminumhoneycomb of Hexcell Aerospace Corp.

Support layer:

Kraft paper Blended paper of 75% cotton and 25% kraft Table 2 belowshows preferred values of spin-casting velocities employed with thematerials of Table 1.

TABLE 2 Cylinder radius, Spin-casting Table 3 shows the casting timesfor typical materials of Table 1, with a shell wall thickness of about0.050 inch.

TABLE 3 Casting time Temp., F. each wall, hrs. 75 About 6-7 140 About3-4 200 About 1-2 TABLE 4 Support layer Spin casting material: velocityr.p.m.

Kraft paper Cotton/kraft paper blend 75/25 About 1000 Synthetic fabricssuch as rayon,

Dacron, nylon, polyester About 500 Industrial glass fabrics such as#181- 139 or #025 of Bay Mills glass fibre matting About 500 Othernon-plastic layers may be applied over the inner and outer shells, suchas thin sheet metal and another embodiment may comprise a thin metalouter laminae or shell having a layer of core material bonded theretoand an inner plastic shell formed against the core layer by the use of asupport layer. Curable thermosetting compounds have been particularlydescribed for use in the products of the inner shell, but thermoplasticmaterials and cementious materials can also be employed that exhibit theviscosity for satisfactory flow to form a uniform cylinder at spinvelocities that are practical for typical commercial processes.

I claim:

1. A process for the manufacture of a cylinder comprising spaced innerand outer concentric cylindrical shells of which at least the innershell is formed of fiowable solidifiable material and which have bondedthereto an interposed core of open-cell type material disposed with thecell ends opening radially and closed by the shells, the processincluding the steps of;

(a) providing the said outer shell,

(b) applying and bonding to the inner cylindrical sur-v face of theouter shell a layer of said core material,

(0) applying to the inner surface of the core material layer a thinsupport layer porous to the solidifiable material and which is elfectiveto prevent excessive percolation of the fiowable material into the corematerial, but is sufliciently porous to be completely impregnated withthe fiowable material,

(d) rotating the outer shell, the core material and the support layerand forming the inner shell against the said support layer by spincasting from the said fiowable, solidifiable material under settingconditions for the material, with the speed of the said rotation suchthat the solidifiable material penetrates the support material andsolidifies therein without excessive percolation of the solidifiablematerial into the core material.

2. A process as claimed in claim 1, wherein the spin casting causesfiowable, solidifiable material to pass completely through the supportlayer material for bonding the inner shell to the core through thesupport layer.

3. A process as claimed in claim 1, wherein the said outer shell isspun-cast from (fiowable, solidifiable material.

4. A process as claimed in claim 1, wherein the said fiowablesolidifiable material is a thermosetting resin and heat is applied tothe material during the formation of the inner shell to speed the curingthereof.

5. A process as claimed in claim 1, wherein the material of the supportlayer is pre-impregnated with the said fiowable solidifiable material,or a material compatible with the fiowable solidifiable material.

6. A process as claimed in claim 1, wherein the said core material hasthe form of a honeycomb with radially disposed cells of hexagonalcross-section.

References Cited UNITED STATES PATENTS 3/1956 Schulze 264311 12/1961Wiltshire 264-311 FOREIGN PATENTS 27,650 8/1964 Japan 264311 1,324,2733/1963 France 264257 ROBERT F. WHITE, Primary Examiner T. P. PAVELKO,Assistant Examiner U.S. Cl. X.R. 264257, 270, 311

